Hi Behnaz, despite Ruud's ...

Hi Behnaz, despite Ruud's concerns about adding methane to the atmosphere, anaerobic ponds are one of the environmentally friendly approaches to removing phosphorous from waste water. (A cattle feed lot produces significantly more methane than an anaerobic pond in a wastewater treatment works).  Your pond's depth of 4m should be adequate for an anaerobic pond, although 5m would be preferable.  If you intend to put baffels into the existing aerated lagoon to separate the different process units you would need to assess the design volumes required for each process and assess whether you have sufficient volume, alternatively you may need to construct a new anaerobic basin ahead of the existing lagoon. In terms of treatment processes, the UCT process or the Johannesburg process can be recommended. Both these give a fair amount of control to the operator to achieve the desired final effluent quality.